> A unique feature of JPEG XL is that it is possible to recompress existing JPEG images (of which there are a lot out there!) to a JPEG XL file that is on average about 20% smaller, without introducing any loss. In fact, the bit-exact same JPEG file can be reconstructed from the JPEG XL file.
I wasn't aware of this and this is actually crazy, and freaking brilliant from a migration point of view. I wonder how that was achieved. I didn't care so much about JPEG XL, now thanks to Google derping I want it everywhere.
The journey to JPEG XL started with guetzli (which started with butteraugli to guide loss in JPEG encoding) and brunsli. Guetzli is a great (but very very slow) JPEG encoder. Brunsli is a classic JPEG1 recompressor. We mixed those and got the first version of PIK. We added some forced format-level progression, adaptive quantization, filtering, larger DCTs, integerated HUIF as lossless/super-progressive coder, and adopted some WebP lossless features into HUIF (Select, 2d-LZ77, entropy clustering).
The final version still had brunsli-like features and we surfaced those as a JPEG recompression system.
I wasn't aware of this and this is actually crazy, and freaking brilliant from a migration point of view. I wonder how that was achieved. I didn't care so much about JPEG XL, now thanks to Google derping I want it everywhere.